Many types of semiconductor integrated circuit chips (herein after called "chips"), particularly memory chips, require for their successful operation an electrically reliable backside contact to the receiving surface to which the chip is attached. Excessive resistance (especially if this electrical resistance varies with changes in temperature) may lead to erratic device performance, or even worse, the circuit may not operate at all due to backside bias voltage fluctuations. It therefore becomes vitally important to achieve as nearly as possible ohmic contact between the backside of the chip and the substrate or receiving surface. Unfortunately this condition is not easily achieved. In many cases contaminants from the wafer fabrication process, if not entirely removed, may provide a source of foreign atoms which "dope" the backside. Gold applied to the wafer backside or from the die attach material also lends an undesirable doping effect tending to alter p-silicon to n-type. There are other problems, less understood which in normal wafer fabrication also detrimentally affect backside contact, such as mechanical damage or inherent properties of the base material.
The above non-ohmic contact problems may be overcome by intentional elemental additions to the die attach preform material or directly to the wafer backside. In fact at least two such techniques are known and commonly used in the art. Borongold-silicon alloy die attach preforms are available and provide p-type doping to insure that p-silicon does not combine to form any unwanted n-junctions on the wafer backside. Similarly, phosphorus-gold-silicon, arsenic-gold-silicon, and vanadium-gold-silicon preforms insure that n-silicon does not combine with any p-type contaminants to form unwanted p-junctions. The other method of providing intentional doping makes use of ion implantation directly into the wafer backside, enriching the p-silicon with p-type ions or the n-silicon with additional n-type. These methods have proved to be only marginally successful however, in terms of the preform doping approach, and very costly if ion implantation is employed. The present invention overcomes completely the drawbacks of the prior art and offers a simplified method of obtaining essentially ohmic contact between silicon wafer backsides and a receiving surface or substrate, being equally advantageous in conventional gold-silicon eutectic alloy or conductive polymer die attachment.